Drive control device of a brushless DC motor

ABSTRACT

A drive control device of a motor includes a comparison unit for comparing a first voltage value, which increases or decreases depending on a current value obtained in an inverter unit of the motor, with a reference voltage value, and an arithmetic processing unit for determining presence or absence of an overcurrent based on a comparison result of the comparison unit. The arithmetic processing unit includes a first terminal and a second terminal. The comparison result of the comparison unit is inputted to the first terminal. The second terminal receives the input of the first voltage value and outputs an operation confirmation signal to the comparison unit at predetermined timings. The arithmetic processing unit determines an overcurrent state based on the first voltage value and determines a state of the first terminal based on an output timing of the operation confirmation signal from the second terminal.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present disclosure relates to a drive control device of a brushlessDC motor.

2. Description of the Related Art

In the related art, there is known a drive control device for driving abrushless DC motor, which has function of stopping the motor for asafety purpose when an overcurrent is generated within the motor. Thedrive control device includes a current detection circuit arranged todetect a current value of a current flowing within the motor.

In the drive control device of the brushless DC motor, the current valuedetected by the current detection circuit is monitored by amicrocomputer. Thus, when an overcurrent is generated within the motor,it is possible to take a measure of stopping the motor or othermeasures. In addition to the microcomputer, it is thinkable to provide acomparison circuit which compares the current value detected by thecurrent detection circuit with a predetermined threshold value. If thecomparison circuit is provided outside the microcomputer, it is possibleto reduce the load borne by the microcomputer.

However, when an abnormality such as a short-circuit, an earth fault oran open state is generated in the comparison circuit, there is apossibility that it becomes impossible to detect the presence or absenceof an overcurrent. For that reason, it is preferable to periodicallyself-diagnose whether the comparison circuit is normally operated.

There is a demand for a drive control device of a motor that can enjoyhigh stability while reducing the number of used terminals of amicrocomputer.

SUMMARY OF THE INVENTION

According to one aspect of the present disclosure, there is provided adrive control device of a brushless DC motor. The drive control deviceincludes a control circuit which includes a comparison unit configuredto compare a first voltage value with a reference voltage value and anarithmetic processing unit configured to determine presence or absenceof an overcurrent based on a comparison result of the comparison unit.The first voltage value increases or decreases depending on a currentvalue obtained in an inverter unit for driving the brushless DC motor.The arithmetic processing unit includes a first terminal to which thecomparison result of the comparison unit is inputted, an overcurrentdetection processing unit configured to determine an overcurrent stateand stop the drive of the brushless DC motor if the first voltage valueexceeds the reference voltage value in the comparison result, a secondterminal configured to receive the input of the first voltage value andrepeatedly output an operation confirmation signal to the comparisonunit at predetermined timings, and an operation confirmation processingunit configured to determine a state of the first terminal based on anoutput timing of the operation confirmation signal.

The above and other elements, features, steps, characteristics andadvantages of the present invention will become more apparent from thefollowing detailed description of the preferred embodiments withreference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view illustrating the configuration of a drive controldevice according to a preferred embodiment.

FIG. 2 is a view illustrating the configuration of a control circuit inmore detail than FIG. 1.

FIG. 3 is a view illustrating operation timings of respective processingunits of a microcomputer according to a preferred embodiment.

FIG. 4 is a flowchart illustrating the operation of a control circuitwhen a motor is driven according to a preferred embodiment.

FIG. 5 is a flowchart illustrating the operation of an operationconfirmation processing unit during a determination process according toa preferred embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An exemplary preferred embodiment of the present disclosure will now bedescribed with reference to the accompanying drawings.

1. Configuration of Drive Control Device

First, the configuration of a drive control device will be describedwith reference to FIG. 1. FIG. 1 is a view illustrating theconfiguration of a drive control device 1 according to one preferredembodiment of the present disclosure. The drive control device 1 is adevice which controls the drive of a motor 9 by supplying a drivecurrent S32 to the motor 9. The drive control device 1 is used tocontrol a motor 9 which operates, for example, a blower of a bathroomdryer. However, the motor to be controlled by the drive control deviceof the present disclosure may be a motor mounted to a product other thanthe bathroom dryer.

In the preferred embodiment, a three-phase brushless DC motor is used asthe motor 9. The motor 9 preferably includes stator coils of respectivephases, namely a U-phase, a V-phase and a W-phase. If a drive current issupplied to the stator coils of the respective phases, a torque isgenerated between a stator and a rotor. Thus, the rotor is rotationallydriven. However, the motor to be controlled by the drive control deviceaccording to the present disclosure may be any motor that uses aninverter, such as a single-phase motor or a brush motor.

As illustrated in FIG. 1, the drive control device 1 preferably includea power supply unit 2, an inverter unit 3 and a control circuit 4.

The power supply unit 2 preferably includes an AC power source 21, adiode bridge 22 and a smoothing capacitor 23. An external power supplydevice may be used as the AC power source 21. The diode bridge 22 is afull-wave rectifier circuit having four diodes. The AC power source 21is arranged to input an AC voltage to between two input terminals 221 ofthe diode bridge 22. Then, the AC voltage thus inputted is full-waverectified in the diode bridge 22. A full-wave rectified voltage having avoltage waveform of only a positive voltage is outputted to between twooutput terminals 222 of the diode bridge 22.

The smoothing capacitor 23 is arranged to smooth the full-wave rectifiedvoltage full-wave rectified in the diode bridge 22, thereby convertingthe full-wave rectified voltage to a DC voltage Vbus. Thus, the DCvoltage Vbus is supplied to a voltage input terminal 31 of the inverterunit 3.

The inverter unit 3 is arranged to supply a drive current S32 to themotor 9 in response to a pulse signal S45 inputted from the controlcircuit 4. The inverter unit 3 preferably includes a voltage inputterminal 31, six switching elements Tu1, Tu2, Tv1, Tv2, Tw1 and Tw2, ashunt resistor Rs, and three motor connection terminals 32 u, 32 v and32 w. Each of the switching elements Tu1, Tu2, Tv1, Tv2, Tw1 and Tw2 isformed of a transistor and a diode which are connected in parallel. Forexample, an IGBT (Insulated Gate Bipolar Transistor) is used as thetransistor.

Two switching elements Tu1 and Tu2 of the six switching elements Tu1,Tu2, Tv1, Tv2, Tw1 and Tw2 are serially connected between the voltageinput terminal 31 and the shunt resistor Rs. Furthermore, another twoswitching elements Tv1 and Tv2 are serially connected between thevoltage input terminal 31 and the shunt resistor Rs. Moreover, theremaining two switching elements Tw1 and Tw2 are serially connectedbetween the voltage input terminal 31 and the shunt resistor Rs. The twoswitching elements Tu1 and Tu2, the two switching elements Tv1 and Tv2,and the two switching elements Tw1 and Tw2 are parallel-connected to oneanother.

The shunt resistor Rs is connected at one end to the switching elementsTu2, Tv2 at one end thereof and Tw2 and is grounded at the other end.When driving the motor 9, a bus current Ibus flows from the inverterunit 3 to the shunt resistor Rs. A motor connection terminal 32 u ispositioned between the two serially-connected switching elements Tu1 andTu2. A motor connection terminal 32 v is positioned between the twoserially-connected switching elements Tv1 and Tv2. A motor connectionterminal 32 w is positioned between the two serially-connected switchingelements Tw1 and Tw2.

When driving the motor 9, with respect to the respective phases, namelythe U-phase, the V-phase and the W-phase, a pair of pulse signals S45 isinputted to a pair of switching elements Tu1 and Tu2, a pair ofswitching elements Tv1 and Tv2 and a pair of switching elements Tw1 andTw2. Thus, the on/off states of the respective switching elements Tu1,Tu2, Tv1, Tv2, Tw1 and Tw2 are switched and the drive current S32 isoutputted from the motor connection terminals 32 u, 32 v and 32 w to therespective phases, namely the U-phase, the V-phase and the W-phase, ofthe motor 9.

The control circuit 4 is a circuit for controlling the inverter unit 3while monitoring the bus current Ibus of the motor 9. FIG. 2 is a viewillustrating the configuration of the control circuit 4 in more detailthan FIG. 1. As illustrated in FIGS. 1 and 2, the control circuit 4preferably includes a shunt voltage terminal 41, a current detectionunit 42, a comparison unit input terminal 43, a comparison unit 44 and amicrocomputer 45.

The shunt voltage terminal 41 is connected between the three switchingelements Tu2, Tv2 and Tw2 of the inverter unit 3 and the shunt resistorRs. If the bus current Ibus flows through the shunt resistor Rs, thevoltage value of the shunt voltage terminal 41 becomes a shunt voltageVs which increases or decreases depending on the current value of thebus current Ibus.

The current detection unit 42 is an amplifier circuit which amplifiesthe shunt voltage Vs inputted to the shunt voltage terminal 41. Asillustrated in FIG. 2, in the preferred embodiment, the currentdetection unit 42 is a differential amplifier circuit which includes anoperational amplifier OP1 as an amplifier and a plurality of resistors.A non-inverting input terminal of the operational amplifier OP1 isconnected to the shunt voltage terminal 41 via a resistor. An invertinginput terminal of the operational amplifier OP1 is grounded via aresistor. Thus, a first voltage value S42 proportional to a voltagedifference between the shunt voltage Vs and the ground voltage isoutputted to an output terminal of the current detection unit 42.

The comparison unit input terminal 43 serves as an output terminal ofthe current detection unit 42 and an input terminal of the comparisonunit 44. The first voltage value S42 outputted from the currentdetection unit 42 is inputted to the comparison unit 44 via thecomparison unit input terminal 43.

The comparison unit 44 is a comparison circuit which includes anoperational amplifier OP2. The comparison unit 44 preferably includes avoltage-dividing circuit 441 which inputs a predetermined referencevoltage value S441 to a non-inverting input terminal of the operationalamplifier OP2. The voltage-dividing circuit 441 preferably includes aconstant-voltage source Vd and two resistors R1 and R2. The tworesistors R1 and R2 are serially connected to each other in between theconstant-voltage source Vd and the ground point. The non-inverting inputterminal of the operational amplifier OP2 is connected to between thetwo resistors R1 and R2. Thus, the voltage supplied from theconstant-voltage source Vd is divided according to a resistance ratio ofthe resistor R1 to the resistor R2 and is then inputted to thenon-inverting input terminal of the operational amplifier OP2 as areference voltage value S441 kept constant.

On the other hand, an inverting terminal of the operational amplifierOP2 is connected to the comparison unit input terminal 43. Therefore,when the first voltage value S42 of the current detection unit 42 isinputted to the comparison unit input terminal 43, the operationalamplifier OP2 compares the reference voltage value S441 with the firstvoltage value S42. The operational amplifier OP2 outputs a voltagevalue, which depends on the magnitude relationship of the two inputvoltage values, from the output terminal thereof.

An output terminal 442 of the comparison unit 44 is connected to abelow-described first terminal 51 of the microcomputer 45. Thus, adetermination voltage S44 indicative of the comparison result of thecomparison unit 44 is inputted to the first terminal 51. Specifically,if the first voltage value S42 is smaller than the reference voltagevalue S441, the determination voltage S44 becomes a H (high) level. Ifthe first voltage value S42 is equal to or larger than the referencevoltage value S441, the determination voltage S44 becomes an L (low)level which is lower than the H level.

The microcomputer 45 is an arithmetic processing unit (microcontroller)which controls the operations of the six switching elements Tu1, Tu2,Tv1, Tv2, Tw1 and Tw2 of the inverter unit 3. The microcomputer 45outputs pulse signals S45 to the inverter unit 3, based on the motordrive command signal inputted from the outside, the determinationvoltage S44 inputted from the first terminal 51 and the first voltagevalue S42 inputted from the second terminal 52.

The pulse signals S45 are three pairs of PWM signals, i.e., six PWMsignals in total, corresponding to the respective phases, namely theU-phase, the V-phase and the W-phase, of the motor 9. The pulse signalsS45 outputted from the microcomputer 45 are respectively inputted to thesix switching elements Tu1, Tu2, Tv1, Tv2, Tw1 and Tw2.

The microcomputer 45 preferably includes a first terminal 51 and asecond terminal 52. The first terminal 51 is a digital port. The secondterminal 52 is a digital/analog port. The first terminal 51 is aterminal to which at least a signal coming from the outside can beinputted. The determination voltage S44 coming from the comparison unit44 is inputted to the first terminal S1. The second terminal 52 is aterminal to which a signal coming from the outside can be inputted andfrom which a signal can be outputted to the outside. That is to say, themicrocomputer 45 is capable of setting the second terminal 52 as ananalog input terminal or setting the second terminal 52 as a digitaloutput terminal.

The second terminal 52 periodically outputs an operation confirmationsignal S52 to the comparison unit input terminal 43 at predeterminedtimings. Thus, the operation confirmation signal S52 is inputted to thecomparison unit 44. Except when the operation confirmation signal S52 isoutputted, the first voltage value S42 coming from the current detectionunit 42 is inputted to the second terminal 52 as an analog quantity.That is to say, the second terminal 52 receives the input of the firstvoltage value S42 except when the operation confirmation signal S52 isoutputted.

In the preferred embodiment, the microcomputer 45 can outputs at leasttwo signals differing in voltage value from the second terminal 52.Specifically, the microcomputer 45 can output, from the second terminal52, two kinds of signals, namely a signal of a permissible level havinga voltage value lower than the reference voltage value S441 and a signalof an overcurrent-equivalent level having a voltage value higher thanthe reference voltage value S441.

As conceptually illustrated in FIG. 2, the microcomputer 45 preferablyincludes a current value detection processing unit 450, a pulse signalgeneration unit 451, an overcurrent detection processing unit 452, andan operation confirmation processing unit 453. The respective functionsof the current value detection processing unit 450, the pulse signalgeneration unit 451, the overcurrent detection processing unit 452 andthe operation confirmation processing unit 453 are realized as themicrocomputer 45 executes arithmetic processing according to apredetermined program.

The current value detection processing unit 450 acquires the firstvoltage value S42 inputted from the current detection unit 42 to thesecond terminal 52 and detects the value of the bus current Ibus basedon the first voltage value S42. The acquisition of the first voltagevalue S42 is executed in synchronism with the pulse signals S45. Thepulse signal generation unit 451 outputs the pulse signals S45 to theinverter unit 3, based on the motor drive command signal (not shown)inputted from the outside and the bus current Ibus detected by thecurrent value detection processing unit 450.

The overcurrent detection processing unit 452 detects a so-called“overcurrent” state, in which the bus current Ibus of the motor 9becomes an abnormally high value, based on the comparison result of thecomparison unit 44. In the preferred embodiment, the overcurrentdetection processing unit 452 always monitors the presence or absence ofan overcurrent during the time when the below-described operationconfirmation processing unit 453 is not operated. Specifically, when thesecond terminal 52 is set as an input terminal, the overcurrentdetection processing unit 452 determines whether the determinationvoltage S44 of the comparison unit 44 inputted to the first terminal 51is at an L level or at a H level.

If the determination voltage S44 is at the L level during the detectionprocess, the overcurrent detection processing unit 452 determines thatthe bus current Ibus of the motor 9 is in an overcurrent state. In thatcase, the overcurrent detection processing unit 452 stops the output ofthe pulse signals S45 from the pulse signal generation unit 451, therebystopping the drive of the motor 9. That is to say, the overcurrentdetection processing unit 452 stops the drive of the motor 9 if it isdetermined that the bus current Ibus of the motor 9 is in an overcurrentstate.

On the other hand, if the determination voltage S44 is at the H levelduring the detection process, the overcurrent detection processing unit452 determines that the bus current Ibus of the motor 9 falls within anormal range. In that case, the overcurrent detection processing unit452 does not stop the operation of the pulse signal generation unit 451.Thus, the pulse signal generation unit 451 continues to output the pulsesignals S45 to the inverter unit 3.

The operation confirmation processing unit 453 performs a determinationprocess of confirming at a predetermined timing whether the comparisonunit 44 is normally operated. Specifically, the microcomputer 45temporarily invalidates the detection process of the overcurrentdetection processing unit 452 at a predetermined timing. Themicrocomputer 45 outputs the operation confirmation signal S52 from thesecond terminal 52 and causes the operation confirmation processing unit453 to perform a determination process.

FIG. 3 is a view illustrating the respective operation timings of thecurrent value detection processing unit 450, the overcurrent detectionprocessing unit 452 and the operation confirmation processing unit 453in the microcomputer 45. As illustrated in FIG. 3, the current valuedetection processing unit 450 performs a detection process of the buscurrent Ibus at predetermined time intervals. In FIG. 3, the period ofthe detection process of the current value detection processing unit 450is set at 40 microseconds. The microcomputer 45 causes the operationconfirmation processing unit 453 to perform the determination processduring the time period in which the detection process is not performedby the current value detection processing unit 450. In the preferredembodiment, the determination process is performed once by the operationconfirmation processing unit 453 during the time when the detectionprocess is performed multiple times by the current value detectionprocessing unit 450.

As illustrated in FIG. 3, the overcurrent detection processing unit 452always performs the overcurrent detection process during the time whenthe determination process is not performed by the operation confirmationprocessing unit 453. The microcomputer 45 temporarily stops thedetection process performed by the overcurrent detection processing unit452, during the time when the determination process is performed by theoperation confirmation processing unit 453.

2. Operation of Control Circuit

Next, the operation of the control circuit 4 will be described withreference to FIGS. 4 and 5. FIG. 4 is a flowchart illustrating theoperation of the control circuit 4 when the motor 9 is driven. FIG. 5 isa flowchart illustrating the operation of the operation confirmationprocessing unit 453 during the determination process.

The control circuit 4 determines whether an overcurrent is generatedwithin the motor 9, using the current detection unit 42 and thecomparison unit 44, which are electric circuits other than themicrocomputer 45, and the microcomputer 45. When the overcurrent stateis detected through the electric circuits in this way, if the electriccircuits are out of order and if a short-circuit, an earth fault or anopen state is generated, there is a possibility that it becomesimpossible to detect an overcurrent within the motor 9.

Moreover, the control circuit 4 determines whether a failure isgenerated in the electric circuits other than the microcomputer 45 ofthe control circuit 4, by outputting the operation confirmation signalS52 from the second terminal 52 of the microcomputer 45 and performingthe determination process using the operation confirmation processingunit 453. Specifically, the current value detection process, theovercurrent detection process and the determination process for theoperation confirmation are performed by the control circuit 4 in thefollowing procedure when the motor 9 is driven.

As illustrated in FIG. 4, if the pulse signal generation unit 451 startsto output the pulse signals S45 to the inverter unit 3, themicrocomputer 45 initially resets the count number N to 1 (step ST101).Furthermore, time t is reset to 0 (step ST102). The time t isincremented every 1 microsecond.

If the setting of the count number N and the time t is completed. Thecurrent value detection processing unit 450 performs the detectionprocess of the bus current Ibus (step ST103). At step ST103, the currentvalue detection processing unit 450 detects the value of the bus currentIbus based on the first voltage value S42 inputted to the secondterminal 52. The value of the bus current Ibus thus detected is used togenerate the pulse signals S45 in the pulse signal generation unit 451.

In the preferred embodiment, the detection process of the bus currentIbus is completed by about 8 microseconds. After step ST103 iscompleted, the microcomputer 45 stops the detection process performed bythe current value detection processing unit 450.

If the detection process of step ST103 is completed, the microcomputer45 determines whether the count number N is 1 (step ST104). If it isdetermined at step ST104 that the count number N is 1, the microcomputer45 causes the operation confirmation processing unit 453 to perform thedetermination process (step ST105). The detailed procedure of thedetermination process will be described later. In the preferredembodiment, the determination process is completed by about 4microseconds. The microcomputer 45 stops the detection process of theovercurrent detection processing unit 452 during the time when thedetermination process is performed.

On the other hand, if it is determined at step ST104 that the countnumber N is not 1, the microcomputer 45 performs step ST106 withoutperforming step ST105.

If the determination process of step ST105 is completed or if it isdetermined at step ST104 that the count number N is not 1, themicrocomputer 45 determines whether the time t is 40 or more (stepST106). That is to say, the microcomputer 45 determines whether 40microseconds is elapsed from the reset of the time t performed at stepST102. If the time t is less than 40, the microcomputer 45 returns tostep ST106 and waits.

If it is determined at step ST106 that the time t is equal to or morethan 40, the microcomputer 45 increments the count number N (stepST107). Thereafter, the microcomputer 45 determines whether the countnumber N is larger than 4 (step ST108).

If it is determined at step ST108 that the count number N is equal to orsmaller than 4, the microcomputer 45 returns to step ST102. Then, themicrocomputer 45 repeats the processes of steps ST102 to ST107. In thiscase, if the count number N is 2 to 4, it is determined at step ST104that the count number N is not 1. Therefore, the determination processof step ST105 is omitted.

On the other hand, if it is determined at step ST108 that the countnumber N is larger than 4, the microcomputer 45 returns to step ST101and performs the reset of the count number N.

As described above, in the preferred embodiment, the determinationprocess is performed once by the operation confirmation processing unit453 during the time when the detection process is performed four timesby the current value detection processing unit 450. Alternatively, thedetermination process may be performed once by the operationconfirmation processing unit 453 during the time when the detectionprocess is performed once to three times by the current value detectionprocessing unit 450. Moreover, the determination process may beperformed once during the time when the detection process is performedmultiple times of five times or more. In order to reduce the load borneby the microcomputer, it is preferred that the frequency of thedetermination process is reduced as long as the safety can be secured.

Subsequently, the determination process of step ST105 performed by theoperation confirmation processing unit 453 will be described withreference to FIG. 5. If a failure is generated in the current detectionunit 42 and if a short-circuit, an earth fault or an open state isgenerated, the first voltage value S42 acquired by the current valuedetection processing unit 450 remains unchanged. Thus, the microcomputer45 can recognize an abnormality. However, if a failure is generated inthe comparison unit 44, it is difficult for the microcomputer 45 torecognize an abnormality. Thus, in the control circuit 4, thedetermination process is performed by the operation confirmationprocessing unit 453 to determine whether a failure is generated in thecomparison unit 44.

If the output terminal 442 of the comparison unit 44 undergoes ashort-circuit, the voltage inputted to the first terminal 51 becomesequal to or higher than the H level of the determination voltage S44.For that reason, the microcomputer 45 cannot detect an overcurrent stateand continues to output the pulse signals S45. On the other hand, if theoutput terminal 442 of the comparison unit 44 undergoes an earth fault,the voltage inputted to the first terminal 51 becomes equal to or lowerthan the L level of the determination voltage S44. Thus, themicrocomputer 45 determines that an overcurrent state is generated, andstops the output of the pulse signals S45. Furthermore, if the outputterminal 442 of the comparison unit 44 is in an open state, the voltageinputted to the first terminal 51 becomes indefinite regardless of thevoltage value inputted to the comparison unit input terminal 43. In thatcase, there is a possibility that the microcomputer 45 cannot properlydetect an overcurrent state and may continue to output the pulse signalsS45.

In the determination process, the microcomputer 45 initially convertsthe second terminal 52 from an analog input terminal to a digital outputterminal (step ST201). Then, the operation confirmation processing unit453 causes the second terminal 52 to output an operation confirmationsignal S52 of an overcurrent-equivalent level having a voltage valuehigher than the reference voltage value S441 (step ST202). When theoperation confirmation signal S52 of an overcurrent-equivalent level isinputted to the comparison unit input terminal 43, if the comparisonunit 44 has no abnormality, the determination voltage S44 outputted fromthe comparison unit 44 becomes an L level. The operation confirmationprocessing unit 453 determines whether the determination voltage S44outputted from the comparison unit 44 is changed to an L level (stepST203).

If the determination voltage S44 outputted from the comparison unit 44is not changed to an L level at step ST203, it is highly likely that ashort-circuit is generated in the comparison unit 44 or that thecomparison unit 44 is in an open state. Thus, the operation confirmationprocessing unit 453 determines that the comparison unit 44 is in anabnormal state, and terminates the determination process. Then, theoperation confirmation processing unit 453 stops to output the pulsesignals S45 from the pulse signal generation unit 451 to the inverterunit 3.

On the other hand, if the determination voltage S44 outputted from thecomparison unit 44 is changed to an L level at step ST203, the operationconfirmation processing unit 453 causes the second terminal 52 to outputan operation confirmation signal S52 of a permissible level having avoltage value lower than the reference voltage value S441 (step ST204).When the operation confirmation signal S52 of a permissible level isinputted to the comparison unit input terminal 43, if the comparisonunit 44 has no abnormality, the determination voltage S44 outputted fromthe comparison unit 44 becomes a H level. The operation confirmationprocessing unit 453 determines whether the determination voltage S44outputted from the comparison unit 44 is changed to a H level (stepST205).

If the determination voltage S44 outputted from the comparison unit 44is not changed to a H level at step ST205, it is highly likely that anearth fault is generated in the comparison unit 44 or that thecomparison unit 44 is in an open state. Thus, the operation confirmationprocessing unit 453 determines that the comparison unit 44 is in anabnormal state, and terminates the determination process. Then, theoperation confirmation processing unit 453 stops to output the pulsesignals S45 from the pulse signal generation unit 451 to the inverterunit 3.

On the other hand, if the determination voltage S44 outputted from thecomparison unit 44 is changed to a H level at step ST205, themicrocomputer 45 converts the setting of the second terminal 52 from anoutput terminal to an input terminal (step ST206). The microcomputer 45determines that the comparison unit 44 is in a normal state, andterminates the determination process.

In this way the drive control device 1 can perform the operationconfirmation as to whether the comparison unit 44 for detecting anovercurrent is normally operated. In the drive control device 1, thesame terminal of the microcomputer 45 is used in inputting the firstvoltage value S42 from the current detection unit 42 and outputting theoperation confirmation signal S52. This makes it possible to reduce thenumber of used terminals of the microcomputer 45.

Particularly, in the preferred embodiment, the drive control device 1causes the operation confirmation processing unit 453 to perform thedetermination process while stopping the detection process of theovercurrent detection processing unit 452. Thus, there is no possibilitythat the drive of the brushless DC motor 9 is erroneously stopped by thehigh voltage signal outputted from the second terminal 52 during thedetermination process.

Furthermore, in the preferred embodiment, the drive control device 1causes the current value detection processing unit 450 to perform thedetection process at predetermined time intervals. The operationconfirmation processing unit 453 performs the determination processusing the time between the predetermined time intervals. Thus, it ispossible to confirm the operation of the comparison unit 44 withoutreducing the operation frequency of the current value detectionprocessing unit 450.

As illustrated in FIG. 2, in the preferred embodiment, the operationalamplifier OP1 as an amplifier and the operational amplifier OP2 includedin the comparison unit are serially connected to each other. By doingso, as compared with a case where the two operational amplifiers OP1 andOP2 are connected in parallel, it is possible to simplify the circuitconfiguration.

3. Modification

While one exemplary preferred embodiment of the present disclosure hasbeen described above, the present disclosure is not limited to theabove-described embodiment.

In the aforementioned embodiment, the second terminal always receivesthe input of the first voltage value S42 except when the operationconfirmation signal S52 is outputted. Alternatively, the second terminal52 may not perform the input and the output during a period except theperiod in which the operation confirmation signal S52 is outputted fromthe second terminal 52 and the period in which the first voltage valueS42 is inputted to the second terminal 52.

The second terminal 52 may continuously and sequentially output theoperation confirmation signal S52 of an overcurrent-equivalent level andthe operation confirmation signal S52 of a permissible level.Furthermore, the second terminal 52 may intermittently and sequentiallyoutput the operation confirmation signal S52 of anovercurrent-equivalent level and the operation confirmation signal S52of a permissible level.

The detailed configuration of the drive control device may differ fromthe circuit configuration illustrated in FIGS. 1 and 2. Furthermore, thetime required in the overcurrent detection process and the operationconfirmation may differ from the time of the aforementioned embodiment.

The drive control device of the present disclosure can be used in, forexample, a drive control device of a brushless DC motor.

Features of the above-described preferred embodiment and themodifications thereof may be combined appropriately as long as noconflict arises.

While preferred embodiments of the present invention have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing from the scopeand spirit of the present invention. The scope of the present invention,therefore, is to be determined solely by the following claims.

What is claimed is:
 1. A drive control device of a brushless DC motor,comprising: a control circuit including a comparison unit configured tocompare a first voltage value, which increases or decreases depending ona current value obtained in an inverter unit for driving the brushlessDC motor, with a reference voltage value, and an arithmetic processingunit configured to determine presence or absence of an overcurrent basedon a comparison result of the comparison unit, wherein the arithmeticprocessing unit includes: a first terminal to which the comparisonresult of the comparison unit is inputted, an overcurrent detectionprocessing unit configured to determine an overcurrent state and stopthe drive of the brushless DC motor if the first voltage value exceedsthe reference voltage value in the comparison result, a second terminalconfigured to receive the input of the first voltage value andrepeatedly output an operation confirmation signal to the comparisonunit at predetermined timings, and an operation confirmation processingunit configured to determine a state of the first terminal based on anoutput timing of the operation confirmation signal.
 2. The deviceaccording to claim 1, wherein the second terminal is configured toreceive the input of the first voltage value except when the operationconfirmation signal is outputted.
 3. The device according to claim 1,wherein the second terminal is configured to sequentially output atleast two signals differing in voltage value to the comparison unit whenoutputting the operation confirmation signal.
 4. The device according toclaim 1, wherein the arithmetic processing unit is configured to stopprocessing of the overcurrent detection processing unit and performprocessing of the operation confirmation processing unit when theoperation confirmation signal is outputted from the second terminal. 5.The device according to claim 4, wherein the arithmetic processing unitfurther includes a current value detection processing unit configured torepeatedly perform a process of detecting the current value, atpredetermined time intervals, based on the first voltage value, andduring a period in which a detection process is not performed by thecurrent value detection processing unit, the operation confirmationsignal is outputted from the second terminal and a determination processis performed by the operation confirmation processing unit.
 6. Thedevice according to claim 5, wherein the arithmetic processing unit isconfigured such that the determination process is performed once by theoperation confirmation processing unit while the detection process isperformed multiple times by the current value detection processing unit.7. The device according to claim 1, wherein the control circuit furtherincludes an amplifier configured to convert the current value obtainedin the inverter unit to the first voltage value, and the amplifier andthe comparison unit are serially connected to each other.